This invention relates to digitizer tables, and, more particularly, in a cordless digitizing system wherein a cordless stylus having a manually operable button thereon transmits positional pulses to a tablet at a carrier frequency, to apparatus for transmitting status information about the button to the tablet comprising, first status logic associated with the stylus for sensing the present status of the button and for encoding and transmitting the present status of the button as a binary 1 or 0 employing a first unique and recognizable sequence of carrier frequency cycles as a binary "1" and a second unique and recognizable sequence of carrier frequency cycles as a binary "0"; and, second status logic included in association with the tablet for recognizing the first unique and recognizable sequence of carrier frequency cycles to be a binary "1", for recognizing the second unique and recognizable sequence of carrier frequency cycles to be a binary "0", and for determining the present status of the button therefrom.
In a digitizing tablet system, a stylus is moved over the surface of a tablet to input positional information related to an X,Y coordinate system associated with the tablet to a computer connected to the tablet. To allow the user to indicate when positional information is to be taken, and the like, the stylus typically has one or more manually-operable buttons associated with it. Recently, for use with so-called pen-driven computing systems where a digitizing tablet associated with a display is the primary input device for the computer, cordless digitizers having no physical connection between the stylus and the tablet have become the configuration of choice because of their added convenience to the user.
The elements of typical cordless digitizer systems are shown in simplified form in FIGS. 1 and 2. The system of FIG. 1 is directed to the use of a pen-type stylus while the system of FIG. 2 employs a puck-type stylus. The system 10 of FIG. 1 comprises a tablet 12 having a connecting cable 14 (or optical link) to the computer (not shown). There is a pen-type stylus 16 having an above-mentioned button 18 thereon. The system 10' of FIG. 2 again comprises a tablet 12 having a connecting cable 14 (or optical link) to the computer (not shown). In this case, there is a puck-type stylus 16' having a plurality of the above-mentioned buttons 18 thereon. In implementations according to techniques employed by the assignee of this application, the stylus 16, 16' is powered by a small lithium battery of the type employed in hearing aids and the like. Accordingly, it can be appreciated that low power consumption as well as reliability are both important aspects of the manner of operation. The stylus 16, 16' contains a coil (such as that indicated as 19 in FIG. 2) which is driven by a pulse stream 20 as depicted in FIG. 3 for positional sensing purposes. The coil emits a corresponding stream of AC magnetic pulses which are sensed by scanned sensing grids in the tablet. The signals developed in the sensing grids are then employed to determined the position of the stylus 16, 16' on the surface of the tablet 12 according to techniques which are well known to those skilled in the art and which form no part of the present invention.
In one previously employed approach to transmitting the status of the button(s) 18, a pulse stream as depicted in FIG. 4 is employed. The positional sensing pulses 20 are followed by button pulses 22 as twice the frequency of the pulses 20 so as to be distinguishable therefrom. The information on the status of the button(s) 18 is encoded within the pulses 22. Unfortunately, this technique proved to be unreliable in a high noise environment. It also consumed 10% of the available power just for the button encoding process.
Cordless digitizers sold under the Wacom and Kurta tradenames use a variable frequency technique for button encoding. In these approaches, the carrier frequency is changed as a function of button depression. As can be appreciated, if a puck type of stylus is employed with multiple buttons, the circuitry to detect the corresponding multiple changes in the carrier frequency attributable to button pushing without effecting position determination accuracy can become complex. Even with only one button, noise can be a significant factor in such an approach as well.
Separate transmission apparatus for transmitting the button status merely adds to the cost of manufacture, size, power consumption, and complexity of the stylus and is, therefore, not really a viable alternative for solving these problems.
Wherefore, it is the object of the present invention to provide a method for encoding and transmitting button status information from the stylus of a cordless digitizer system which is highly accurate and reliable even in an extreme noise environment.
It is also the object of the present invention to provide a method for encoding and transmitting button status information from the stylus of a cordless digitizer system which does not consume any extra power.
Other objects and benefits of the invention will become apparent from the detailed description which follows hereinafter when taken in conjunction with the drawing figures which accompany it.